1. Field of the Invention
The present invention relates to a wastewater treatment system and method of using same. More particularly, the present invention relates to a new and improved wastewater treatment system having a unique combination of three subsystems for employing biological, microbiological, and mechanical means to remove water contaminants in an aquaculture operation application, and other applications.
2. Description of the Related Art
As health conscious Americans begin to consume more fish products and the naturally occurring sources of fish become depleted, there is a growing need to fill the demand for fish products by turning to aquaculture. Aquaculture is defined as the production and husbandry of aquatic plants and animals in controlled environments. The term husbandry means the application of scientific principles to farming. Controlled environments are directed or regulated production environments ranging from a low level of control, termed xe2x80x9cextensive,xe2x80x9d where limited capital and management are applied, to a high level of control, termed xe2x80x9cintensive,xe2x80x9d where more comprehensive capital and management are applied to production.
Aquaculture has become a one billion dollar industry in the U. S. Nearly 15% of our seafood supplies are currently supplied by aquaculture. Growing at a rate of 20% per year, aquaculture is the fastest growing sector of the agriculture industry. Aquaculture is an ecologically efficient means of providing seafood for American consumers while significantly reducing pressure on our limited wild fisheries resources.
Foreign competition is having a major impact on U.S. aquaculture operations. More than 60% of our seafood supplies are now imported, resulting in a large annual trade deficit ($6.9 billion). A growing fraction of aquaculture imports comes from the warm climates of South America and Asia. These countries have the advantage of lower production costs by using abundant quantities of warm water that are available in the tropics. Often there are few or no environmental laws controlling their discharges which result in environmental degradation and little or no overhead costs associated with complying with environmental laws. Imports of fish grown in Colombia, Costa Rica, Ecuador, Taiwan, China, and Indonesia have increased markedly as the foreign competition adopts new culture technologies, often developed here in the U.S. These competing products are produced with low energy, water, labor, and environmental costs. As a result, many U.S. aquaculture products are not competitive with foreign aquaculture products.
Efficient, economical and productive aquaculture in the United States would meet the growing demands of fish in the American diet, would remove a huge burden on our natural wildlife resources and would also reduce our dependence on imports.
However, the industry of aquaculture is threatened by the environmental pollutants sometimes associated with the discharge of untreated fish farm effluents. The future existence and potential for expansion of the industry is in jeopardy unless methods can be developed to reduce the nutrients in the effluents emanating from fish farms that cause eutrophication in the receiving waters. Cage culture systems and pen culture farms are also hampered by nutrient contamination of ground water aquifers, drinking water reservoirs, and sensitive coastal estuaries. Catfish production in Mississippi is threatened by ground water overdraft, saltwater intrusion, and concerns about potential land subsidence.
Treatment of aquaculture wastewater to meet U.S. Environmental Protection Agency (EPA) effluent discharge regulations requires removal of settleable solids. Often treatment of dissolved nutrients is mandated as well. Many states are developing more rigid standards for biological oxygen demand (BOD), ammonia, total nitrogen, settleable solids, suspended solids, and phosphorus in an effort to prevent eutrophication and further degradation of natural resources. The EPA recently published a notice of proposed rule making in the Federal Register indicating that they will adopt guidelines and standards for effluents from concentrated aquatic animal production facilities by July 2004.
In order to address these issues, a broad spectrum of water treatment equipment has been marketed for years to treat virtually all of the pollutants created by fish and other farmed aquatic animals. However, the equipment currently available is based primarily on technologies developed for municipal sewage treatment that have been designed for heavily concentrated waste streams. Typically, the designs require large capital and operating budgets which can only be borne by governmental agencies and municipalities.
In addition, aquaculture facilities require a much higher degree of water quality for recycling than required by most treated municipal wastewater. Most of the existing technologies are generally not up to the task of producing high quality treated water suitable for aquaculture. In fact, the treated final discharge from a municipal sewage facility is often of poorer water quality than a totally untreated discharge from an aquaculture facility.
In general, intensive water treatment techniques have primarily been applied to closed-system aquaculture production processes. Closed system aquaculture utilizes purified recirculated water in the system. There have been several attempts over the past decade to develop closed system aquaculture operations in the U.S. Intensive, completely recirculated closed systems have been developed for tilapia, sturgeon, striped bass and catfish production.
The high cost of production associated with the expensive water treatment systems create a situation in which the price of the fish produced are not competitive on an open market when compared to fishery products and imports. In order to accommodate the high overhead expenses, many of these operations have resorted to selling product to a limited live fish retail market. These high production costs as well as numerous disease problems and off-flavor problems caused by poor water quality associated with closed systems have demonstrated that this method of production is impractical and unprofitable, at this time.
The use of traditional water treatment technologies has not been successful in commercial production to date and there have been many notable failures by companies attempting to use these methods. Each of the facilities cost millions of dollars to build. The types of treatment technologies that each of these companies utilized relied heavily on industrial design waste treatment components. These methods of waste treatment are expensive to purchase and operate and the resulting poor water quality often leads to disease and off-flavor problems. Even if the machinery functioned as was hoped, the operating costs were too high for what is essentially a farming venture to afford over the long term.
Unfortunately for the aquaculture industry, few manufacturers of biofiltration equipment have been able to develop truly low-cost technologies to meet the needs of this industry. Most existing biofiltration systems have been developed for the municipal sewage and manufacturing waste industries, fields in which significant public tax revenue or private profit margins have been available. The result has been the development of high-tech treatment components constructed of stainless steel or concrete and marketed by engineering companies focused tightly on high profit margin industries such as refineries and haz-mat cleanup. Almost all currently available water treatment equipment is too expensive to purchase and operate, to be useful and economical in the aquaculture industry.
In intensive, closed system aquaculture, the costs for water treatment often exceed $0.0566 per cubic meter ($70 per acre-foot). This is a relatively high cost that may be justifiable for holding broodstock in hatchery operations or for the production of high priced tropical fish held at low densities. However, water pumping or delivery costs for most agricultural commodities are on the order of $0.008-0.012 per cubic meter ($10-15 per acre-foot). Just as is the case with conventional agriculture, large-scale fish production operations require water at or below this cost range in order to remain competitive with the price structure for fish from the domestic commercial fisheries and from imports.
There have been a few efforts to develop intensive tank culture systems that use extensive open ponds for water treatment. However, these recirculated water treatment systems are generally converted fish production ponds which were not designed or managed to maximize water treatment. Two examples are a raceway tank culture system for channel catfish, and a similar system used on a seasonal basis for growing tilapia.
In addition to the problem of waste water treatment for eventual release as well as for use in recirculating closed systems, the future growth of the aquaculture industry in the U.S. is limited by the finite supply of water. Increased demands on surface and ground water resources are reducing the amount of water that can be reasonably used by aquaculture operations. Such pressures make some form of water reuse a prerequisite for long-term survival and expansion of the aquaculture industry.
Every major review of aquaculture has described the critical need for improved aquaculture water treatment systems if this new industry is to continue to expand in the U.S. The National Aquaculture Act and the revised National Aquaculture Plan highlight the importance of this area of aquaculture research and development. The 1994 National Agenda for Aquaculture and the Environment describes the critical need to conserve water and utilize wastes in integrated systems which combine terrestrial agriculture and constructed wetlands. The Congressional Joint Subcommittee on Aquaculture and the National Research Councils promote a xe2x80x9cnational agenda to encourage the development of advanced aquaculture technologies and environmentally sound, renewable resources,xe2x80x9d as part of the Presidential Initiative on Sustainable Development.
Obviously, aquaculture is a water dependent industry. Open systems (in which new water flows through the tanks once and is then discharged as waste) are much less complex and expensive than recirculated systems. Unfortunately, there are only a few sites in the U.S. with sufficient water supplies to support this method of production. In addition, there remains the need to address the issue of solid waste removal from effluents.
At the other extreme, totally closed systems require intensive filtration, which often involves very high capital and operating costs as well as associated poor water quality resulting in high mortality due to disease and off-flavors which affect the marketability of the product.
For these reasons, semi-open systems (in which most but not all of the water is recirculated) hold the key to future expansion of aquaculture in the U.S. The present invention relates to a new and improved semi-open aquaculture system and method of using it. This method of semi-open aquaculture allows fish to be held at high densities in intensive raceways or tanks, while a large fraction of the culture water is recycled through a series of extensive ponds for water treatment. There are several advantages to this approach, including lower costs for utilities, chemical use, and water treatment, and less labor needed for fish transfers and harvests. The cost advantages in treating the recycled water in pond systems rather than in more expensive filtration systems include reduced costs of installation, operation, and maintenance.
The semi-open system approach has very high potential, but there are several aspects which need to be addressed. A successful semi-open system would require a combination of intensive fish holding methods in combination with extensive water treatment methods. While the technology for intensive fish culture has advanced considerably over the past ten years, relatively little work has been directed toward the development of cost-effective extensive water treatment techniques for use in aquaculture. The present invention relates to a new and improved cost effective extensive water treatment system and method of using it.
The problem of finding secondary usage for the portion of the pond-treated water not utilized by recirculating in the aquaculture system would also need to be addressed. At most aquaculture facilities, there is a significant volume of effluent water being discharged, often on a continuous basis.
Since such water poses few human health risks, it should be ideal for other secondary uses, including agricultural irrigation, golf course and landscape irrigation, recreational lakes, and wetland habitat restoration and enhancement. Currently, most of the dissolved wastes are in the form of ammonia, and other nitrogenous wastes. The greater concern in this area is now with the phosphorus compounds, which are generally bound in the solids fraction.
The present invention presents a new and improved method of solid fraction removal from aquaculture effluent and method of using same. This solids fraction of the effluent may be removed by settling ponds stocked with a secondary hardy omnivorous opportunistic fish species. These bottom feeding fish will eat uneaten fish feed as well as fish fecal particulate matter which are produced by the primary production fish. These fish have been proven to be extremely efficient at consuming solids suspended in the wastewater and serve to prevent any appreciable sludge build-up in the treatment system. In practice, the use of the secondary omnivorous fish species results in an ecologically efficient, low maintenance, low cost sludge removal system.
In addition, the biomass of the secondary fish population increases sufficiently to warrant a harvest of the secondary fish as a secondary crop income with minimal or no added costs of production.
If the particulate matter is removed from the effluent, the discharge waters could be used for traditional row crop irrigation. The present invention addresses the problem of shared usage of water utilizing a new and improved method of using nutrient rich fish effluent for use by agriculture. For this use, no further treatment would be required, since the relatively low concentrations of ammonia and nitrate would act as a mild fertilizer that would enhance the production of most vegetable crops. Many fish culture operations are located in major agricultural production regions of the country where this technology could be employed.
By integrating the use of fish farm effluents with agricultural irrigation, both operations could share the water costs which results in a mutually beneficial reduction in production costs. In areas having a finite water supply, total production volumes would be enhanced. Since the only water lost in fish farming is due to evaporation and seepage, nearly all of the discharge water could be consumed by irrigation.
The present invention proposes a new and improved semi-open, cost effective aquaculture system, utilizing a secondary crop fish for solid waste removal and efficient sharing usage of water resources with improved agricultural benefits. Therefore, there would be little or no discharge of nutrients to receiving waters, which would help to eliminate eutrophication and other pollution problems, and would conserve water use in the region. With widespread secondary use of fish farm effluent, freshwater aquaculture could realize its ultimate potential, as a non-consumptive, water dependent activity capable of providing multi-beneficial uses of the country""s finite water resources.
The basic design question for aquaculture water treatment and reuse is whether to attempt to modify and adapt existing municipal treatment technology to fish culture facilities, or to explore new treatment systems specifically designed to remove low concentrations of solids, BOD, ammonia, nitrate, and phosphorus from relatively high volume wastewater streams. In either case, this must be accomplished with substantially less complexity than municipal wastewater treatment, and at costs that could be supported within the low-margin agricultural commodity framework common to most forms of aquaculture.
In general, the systems used for water treatment in closed and semi-closed aquaculture systems have been based on water treatment units initially developed for treatment of municipal wastewater. Chemical treatment technologies are giving way to biological processes, due to cost considerations. Chemical treatment technologies may also create secondary pollution problems. Special physical processes such as reverse osmosis are applicable to providing tertiary water quality for municipal waste treatment where high water costs are not as important, but are completely impractical for agricultural treatment purposes.
There has been increased focus on phosphate pollution from fish culture facilities which contribute to eutrophication of receiving waters. Solids removal is receiving more attention in treatment of aquaculture effluents since phosphates are usually bound with settleable solids. Solids removal technologies involve either physical, chemical or biological removal methods. The physical methods include sedimentation basins, clarifiers, plate/tube separators, and varying filtration technologies, including bead filters. Biological solids removal methods involve anaerobic and facultative bacterial digestion.
Solids removal has not posed as great a problem for aquaculture as does the removal of dissolved nitrogenous compounds. Intensive, high density fish farming, in particular, produce large quantities of nitrogenous waste. In order to maintain high fish poundage production and consistently good tasting food fish, this constant production of nitrogen containing waste must be dealt with immediately and removed from the water coming in contact with fish.
These nitrogen containing compounds, most importantly ammonia, are typically removed utilizing biological treatment, most often with microorganisms, especially bacteria. The two basic processes of ammonia contaminant breakdown consist of nitrification and denitrification. Nitrification breaks down ammonia in solution to nitrate as follows:
NH4+xe2x86x92NO2xe2x88x92xe2x86x92NO3xe2x88x92xe2x80x83xe2x80x83(1)
The oxidation of ammonia to nitrate is a two step sequential biological process involving two different autotrophic bacteria, most commonly of the genuses Nitrosomonas sp. and Nitrobacter sp. which utilize the ammonia as an energy source. The overall simplified reaction for nitrification may be expressed as:
NH4++2O2xe2x86x92NO3xe2x88x92+2H+xe2x86x922H2Oxe2x80x83xe2x80x83(2)
Denitrification then occurs if conditions are such that a denitrification facilitating anaerobic zone is presented. The denitrification process involves a reduction of nitrite to nitrogen gas through the following sequence in which bacteria, preferably heterotrophic bacteria, reduce the nitrate to a lower state of oxidation, expressed as follows:
NO3xe2x88x92xe2x86x92NO2xe2x88x92xe2x86x92NOxe2x86x92N2Oxe2x86x92N2xe2x80x83xe2x80x83(3)
During this reaction heterotrophic bacteria, which use the carbon based material as an energy source, carry out the following simplified overall reaction:
NO3xe2x88x92+6H++5exe2x88x92xe2x86x920.5N2+3H2Oxe2x80x83xe2x80x83(4)
Another significant concern when recirculating aquaculture effluent is the potential for build-up of total carbon dioxide (CO2) produced by fish respiration. Unless free CO2 is actively removed from a culture system, it can quickly increase to toxic levels. Free carbon dioxide and the associated low pH levels are harmful to fish. The present invention presents a new and improved wastewater treatment system facilitating carbon dioxide removal from aquaculture effluent. This novel method of CO2 removal will be of great use to the aquaculture industry because it accomplishes removal of the carbon dioxide in an inexpensive fashion, that does not heavily rely on the continuous addition of expensive chemicals.
Similar to aquaculture, in other water use applications, there are intensive and extensive forms of biological wastewater treatment. Intensive biological treatment involves a high technology, mechanized approach. Bacteria populations can be managed intensively in a suspended mode involving the use of aerated lagoons and oxidation ditches. Another common method for management of bacterial populations is activated sludge processes, on non-submerged media such as trickling filters or rotating biological contactors, or on submerged media such as fluidized beds and packed beds. Extensive biological treatment methods involve the use of a low technology, natural systems approach. The primary extensive methods are slow sand filtration, open ponds, managed algal ponds where algae utilize ammonia and/or nitrate, and constructed wetlands, involving aquatic plants receiving either surface flow or subsurface flow of effluent.
The concept of, and methods for aquacultural fish raising are well known and documented. Examples of different types of devices, methods and systems, water treatment units and techniques that might be suitable for aquaculture are disclosed in U.S. Pat. Nos. 5,820,759, 5,660,142, 5,593,574, 5,582,734, 5,558,763 5,061,368, 5,863,433.
Systems utilizing recycled water as a means of maintaining an aquaculture system have been explored. U.S. Pat. No. 5,820,759 describes such a system. The system contains a water hyacinth system for removal of solid and nitrogenous waste from the effluent from the fish holding area. The system also incorporates an algae based oxygenation system for water treatment.
Hyacinth systems are sensitive to temperatures and therefore their application has been limited primarily to warm weather sites. The hyacinth systems produce a heavy plant canopy which limits wind turbulence and can lead to anaerobic conditions. The high fiber content and metal levels in the plants limit their use as an animal feed supplement. Therefore, the use of water hyacinths to treat aquaculture waste is limited.
Extensive treatment technologies appear to offer the best possibilities for widespread implementation at most U.S. fish farming facilities. Therefore it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which incorporates extensive biological treatment methods for removal of nitrogenous compounds utilizing open-pond treatment systems and employing a broad temperature tolerant plant species.
Also, since the hyacinth system must have shallow water, it is difficult to remove sludge which can lead to clogging of the system and makes it difficult to harvest the plants. Therefore it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products utilizing a novel particulate removal subsystem in addition to a plant-based waste removal subsystem which when working together would be low maintenance, non-fouling, and which would turn waste products into an easily harvested and marketable valuable by-product.
In addition, U.S. Pat. No. 5,820,759 incorporates an algae based treatment for dissolved contaminants as well as a required re-oxygenation of treatment waters. Algae based wastewater treatment systems are also temperature dependent, and work best only during warm weather months, posing severe limitations on year-round production.
Therefore it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which provides a predictable, consistent, stable performance, making year-round production operations optimal.
Another aquaculture system which teaches a closed system of utilizing recirculated treated water is disclosed in U.S. Pat. No. 5,660,142. Therein, a system is provided that incorporates a settling pond in which organic matter from fish pond effluent is partially degraded over a period of time.
The supernatant is fed to a fluidized bed reactor. This system requires an extended period of time in order to complete the solids settling process and the filtration of water by these means. Maintenance of the column used for the denitrification of the effluent would be relatively expensive, and would result in an extended period of time where the system could not be used during maintenance, and which would require multiple redundant fluidized bed columns should this system be used on a large scale, or a growing system scaling up, thus resulting in greatly increased overhead costs.
Therefore, it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which would provide a sequential combination of subsystems for removal of the solid particulate matter as well as the nitrogenous waste in the culture effluent. Furthermore, it would be highly desirable if such a system used a combination of low technology sequential subsystems which would remove a high percentage of contaminant compounds from the effluent, rendering the subsequent treated water useful in recirculation back to culturing operations. It would also be highly desirable if the system provided ease of operation and rapid, low capital methods of expansion to accommodate changing volumes of effluent in scaling up said aquacultural operations.
The aquaculture water treatment system disclosed in U.S. Pat. No. 5,593,574 consists of a fish tank with a double outlet. Solid waste particles are drawn into a central well by a trickle of water and conducted to a spray bar of a separate biofilter apparatus. The water is distributed over a bed of floating media pellets serving as a base for bacterial growth and subsequent nitrification of the incoming wastewater. Removal of solid wastes relies upon a spontaneous clumping of particulates and flushing of the aggregates from the system.
This system is limited by the fact that a spray bar must distribute the initial effluent evenly over the media bed. This will result in a limited amount of water that can the processed at any given point in time. The increased usage of water in a larger system would necessitate multiple such spray bars and beds of media pellets with an additional cost in equipment and maintenance. The spray bar arm is provided with small openings from which the effluent water is emitted, which would lend itself to clogging and more frequent cleaning and higher maintenance costs.
Therefore, it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which would utilize multiple methods of particulate removal, use waste produced in primary operations to produce a secondary marketable aquacultural product to offset overhead costs, provide ease of operation and rapid, and low capital methods of expansion to accommodate changing, increasing volumes of effluent, especially from rapid scaling up of operations.
As previously mentioned, many of the inventive systems utilized by aquaculture up until very recently have been fashioned after equipment systems based on municipal wastewater treatment applications. These systems were designed to process wastewater containing high levels of particulates and contaminants. The resulting treated water was meant to be released into the environment and not particularly designed to meet the high water quality standards required in more sensitive recirculating aquaculture systems. Many of these systems were designed to accommodate large amounts of wastewater and require high capital and high maintenance which would be unfeasible for the relatively low margin agricultural and aquacultural production operations.
The invention in U.S. Pat. No. 5,582,734 describes a municipal wastewater treatment system which relies upon an oxidation ditch to remove settleable solids and nitrogen removal. The process incorporates a mixer in the oxidation ditch which enables independent aeration and mixing. While this process provides for rapid expansion to accommodate changing volumes of effluent, the process is controlled by a microprocessor-based automated control system which could result in high installation, labor and maintenance costs. Additionally, traditional oxidation ditch technology is relatively ineffective in aquaculture applications. The reason for this is in aquaculture effluent there is so little particulate waste that there is insubstantial surface area for the attachment of a bacterial film.
Therefore, it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which would provide ease of operation, low initial capital outlay and low subsequent everyday operating costs.
Another sewage treatment system is described in U.S. Pat. No. 5,558,763 which filters solid components in the wastewater by using a floating filter medium. The system utilizes two air jetting means. The first air jets separate the floating media from solid sewage components and the second air jet ensures that the solid component does not adhere again.
Again, the system here was designed to accommodate wastewater with large amounts of particulate material. The air jets are provided for elimination of the solid component from the wastewater in an efficient manner. Then, a second sedimentation tank with a partitive plate is provided for further sedimentation. The primary concern of this system is efficient removal of large amounts of sediment, which for public health reasons cannot have secondary usage as nutrients for plant or animal populations.
Therefore, it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which would provide a method by which particulates in the wastewater stream would be partially removed by nutrient utilization in plants and animals, producing a secondary harvest of a valuable marketable product, as well as partially purified water for secondary uses and highly purified water for recirculation back into culture operations.
In the above-mentioned patent, the subsequent treated wastewater is not of sufficient quality required in aquaculture recirculation. Thus, it would also be highly desirable that such an inventive system utilize multiple stages, or sequential subsystems, consisting of low technology treatments for removal of dissolved contaminants which could produce off-flavor in primary production fish or render the primary production fish more susceptible to diseases.
U.S. Pat. No. 5,061,368 discloses another system for treating wastewater. In the system, a particulate body formed by covering and fixing nitrifying bacteria is inserted in a nitrifying vessel which includes an air diffusion device for supplying oxygen to the nitrifying bacteria. The wastewater is circulated between the nitrifying vessel unit and a biological reaction vessel.
In this interesting invention, a multiplicity of nitrifying vessels would be required in order to accommodate an increased level of wastewater. In addition, a separate unit is required for anaerobic biological treatment of effluents. Thus, costs of equipment for larger volumes of water treatment would be prohibitive and much time consumed during installation. Any attempt at scaling up operations would greatly increase overall production and overall operating costs.
Therefore, it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which would provide multiple low technology sequential subsystems which would be capable of varying effluent volumes, provide ease of operation, and be readily scalable yet maintain low capital and operating costs of up scaling production.
The use of constructed wetlands for treatment of storn water runoff and municipal wastewater is well known. An efficiently operated constructed wetlands ecosystem can be a cost effective method of ammonia, nitrate and suspended solids removal in treatment of wastewater.
The invention described in U.S. Pat. No. 5,863,433 relates to the design and operation of a constructed subsurface-flow wetlands for such a purpose. This wetland utilizes an undergravel filter to handle large amounts of particulate matter present in municipal waste water. The wetlands disclosed here do not specify any type of aquatic plants for bioremediation of wastewater.
While this novel concept adequately addresses the requirements for treatment of large quantities of municipal wastewater that is high in particulate matter, and the resulting treated water is sufficiently free from harmful contaminants to release into the environment, it would not be sufficient alone to meet the water quality requirements of a recirculating aquaculture system. Moreover, subsurface-flow wetlands can be prone to clogging, but more importantly, are much more capital intensive to construct. They also do not permit gas exchange freely, including exchange of both O2 and CO2, and therefore, by limiting O2, nitrification is limited as well.
Therefore, it would be highly desirable to have a new and improved wastewater treatment system for aquaculture products which would provide a series of low technology sequential treatment stages which would result in an effluent of sufficient quality as required to prevent aquacultural product contamination, off-flavors, parasites, devastating diseases and other related problems associated with intensive fish rearing.
Therefore, the principal object of the present invention is to provide a new and improved semi-open aquaculture wastewater treatment system consisting of a series of cost effective, low technology, sequential water treatment subsystems, having a more effective and efficient means for the removal of particulates and nitrogenous compounds in aquaculture effluents as well as providing a flexible, easily expandable and affordable treatment of wastewater that would be of sufficient quality for use in numerous other applications. Moreover, the principal object of the present invention is to provide a new and improved sequential method of wastewater treatment comprising three wastewater treatment subsystems. The subsystems incorporate a solids/particulate removal subsystem, a suspended media ammonia removal biofilter reactor subsystem, and a constructed wetlands water polishing subsystem to complete the removal of particulates and nitrogenous compounds.
It is a further object of the present invention to provide such a new and improved system for the treatment of wastewater that incorporates a subsystem utilizing an omnivorous secondary fish species for particulate removal solids removal, and which produces a harvestable secondary fish crop for offsetting operating costs. In this subsystem of solids removal, elongated fish raceways stocked with a secondary hardy detritivorous opportunistic fish species, such as tilapia and/or carp, would represent a more effective and efficient removal of solids and particulates from the aquaculture effluent as well as providing a continuous economic gain.
It is yet a further object of the present invention to provide such a new and improved wastewater treatment system in which soluble nitrogenous compounds are readily removed by a subsystem integrating an open-ditch biofilter reactor containing polyurethane foam and/or plastic (such as extruded pipe) suspended support media for the support and growth of microorganisms active in the ammonia removal process. This unique and very effective suspended media ammonia removal technology system is known as the SMART system. The SMART subsystem includes a foam or plastic media providing a floating matrix for the growth of microorganisms including nitrifying bacteria, along with a paddlewheel which provides circulation and aeration of the water, as well as partial removal of solubilized carbon dioxide from wastewater in a cost effective and efficient manner.
It is a further object of the present invention to provide such a new and improved wastewater treatment system and method of making same, that incorporates a constructed wetlands subsystem for further removal of nitrogenous compounds and remaining suspended solids, and which does so by delivering the wastewater to a series of large, shallow earthen ponds containing numerous aquatic plant species which have a broad temperature tolerance. This constructed wetland pond incorporates extensive biological treatment methods for removal of nitrogenous compounds. In this way, this third wastewater treatment subsystem provides a low technology, cost effective and efficient means of further removal of ammonia and remaining suspended solids from aquaculture operations effluents.
It is yet another object of the present invention to provide such a new and improved treatment of wastewater utilizing sequential multiple, low technology, cost effective subsystems in which customized combinations of one or more of each of the novel wastewater treatment system subsystems can be configured, as required by varying applications and climates, as well as varying water resource and aquacultural/agricultural conditions.
Briefly, the above and further objects of the present invention are realized by providing a new and improved system for the treatment of wastewater to enable effective and efficient removal of suspended solids, nitrogenous contaminants such as ammonia, and dissolved carbon dioxide, by using integrated, cost effective, low technology sequential water treatment subsystems.
A novel wastewater treatment system is provided including three subsystems. The first subsystem is comprised of a fish raceway solids removal channel populated with relatively high densities of a detritivorous fish such as tilapia or carp, that have high potential as an efficient means of feeding on, and thereby, removing suspended solids and particulate matter that are present in the primary fish production effluent. This step removes approximately 30% of the suspended solids before further decomposition to form more harmful and toxic compounds such as ammonia. In addition, the present invention accomplishes removal of solids while also allowing production of a secondary crop fish which can be harvested and sold to offset expenses. Moreover, this treatment of wastewater contaminants occurs without the use of potentially polluting chemicals or costly equipment, while facilitating production of the more valuable primary fish crop.
The second wastewater treatment subsystem is comprised of an enhanced form of nitrifying reactor called the Suspended Media Ammonia Removal Technology (SMART) biofilter reactor system. This water treatment component consists of an oval-shaped concrete tank in which the water is circulated by means of a large hydraulic or electrically powered paddlewheel. The water column contains a number of polyurethane foam particles cut into cubes, spheres or other shapes and/or plastic carriers such as cut extruded pipe, that provide an increased well-aerated surface area for the support and growth of microorganisms including nitrifying bacteria. The supported bacteria break down ammonia, the most common and most toxic compound present in fish culture effluent, to less toxic nitrogenous compounds such as nitrate. The SMART biofilter reactor units are capable of removing at least 40% of the total ammonia present in the aquaculture effluent. Furthermore, SMART biofilter reactors are readily and economically scalable to any wastewater treatment application requirements.
The third wastewater treatment subsystem in the novel sequential water treatment process includes a series of constructed wetlands ponds. Pre-treated effluent from the SMART subsystem is delivered to large, shallow earthen ponds that are planted with mature bulrush plants (Scirpus sp.). This water polishing subsystem is capable of removing up to 40% of the remaining ammonia and nearly all of the remaining suspended solids. Moreover, constructed wetland ponds are readily and economically scalable to meet the demands of any wastewater treatment application.